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Abstract

An unnatural increase in primary production is the main driver of accelerated eutrophication, which causes negative impacts in aquatic systems around the world. Studying factors regulating primary production is therefore critical in systems such as Lake Erie, which experiences eutrophication and has been impacted by many stressors. In this thesis, I investigated factors regulating primary production in Lake Erie on both a long-term temporal scale (by comparing summer values from 1970 to 2014/15 in the western basin) and a spatial scale (by comparing nearshore and offshore sites among the three basins). Both studies suggested that multiple stressors, such as changes in nutrient loading, dreissenid grazing, and light penetration, are likely regulating primary production in Lake Erie. Dreissenid grazing and phosphorus loading reductions may have contributed to a long-term decrease in volumetric primary production in the western basin, as well as to similar volumetric primary production between near and offshore sites in all three basins. Meanwhile, a long-term increase in light penetration in the western basin resulted in no significant change in areal primary production since 1970. Increased light penetration in the eastern basin also resulted in no significant difference in areal primary production compared to the other basins, despite significantly lower volumetric primary production in the eastern basin. In the future, nutrient enrichment experiments and annual primary production measurements are needed. This study demonstrates the complexity of factors regulating primary production and the importance of studying these factors to understand drivers of eutrophication and food web dynamics in Lake Erie.